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(;module:
lux
(.. (functor #as F)
(applicative #as A)))
## [Utils]
(def: (fold f init xs)
(All [a b]
(-> (-> b a a) a (List b) a))
(case xs
#;Nil
init
(#;Cons x xs')
(fold f (f x init) xs')))
(def: (map f xs)
(All [a b]
(-> (-> a b) (List a) (List b)))
(case xs
#;Nil
#;Nil
(#;Cons x xs')
(#;Cons (f x) (map f xs'))))
(def: (reverse xs)
(All [a]
(-> (List a) (List a)))
(fold (lambda [head tail] (#;Cons head tail))
#;Nil
xs))
(def: (as-pairs xs)
(All [a] (-> (List a) (List [a a])))
(case xs
(#;Cons x1 (#;Cons x2 xs'))
(#;Cons [x1 x2] (as-pairs xs'))
_
#;Nil))
## [Signatures]
(sig: #export (Monad m)
(: (A;Applicative m)
applicative)
(: (All [a]
(-> (m (m a)) (m a)))
join))
## [Syntax]
(macro: #export (do tokens state)
{#;doc (doc "Macro for easy concatenation of monadic operations."
(do Monad<Maybe>
[y (f1 x)
z (f2 z)]
(wrap (f3 z))))}
(case tokens
(#;Cons monad (#;Cons [_ (#;TupleS bindings)] (#;Cons body #;Nil)))
(let [g!@ (: AST [["" -1 -1] (#;SymbolS ["" "@"])])
g!map (: AST [["" -1 -1] (#;SymbolS ["" " map "])])
g!join (: AST [["" -1 -1] (#;SymbolS ["" " join "])])
g!apply (: AST [["" -1 -1] (#;SymbolS ["" " apply "])])
body' (fold (: (-> [AST AST] AST AST)
(lambda [binding body']
(let [[var value] binding]
(case var
[_ (#;TagS ["" "let"])]
(` (let (~ value) (~ body')))
_
(` (|> (~ value) ((~ g!map) (lambda [(~ var)] (~ body'))) (~ g!join)))
))))
body
(reverse (as-pairs bindings)))]
(#;Right [state (#;Cons (` (;_lux_case (~ monad)
(~ g!@)
(;_lux_case (~ g!@)
{#applicative {#A;functor {#F;map (~ g!map)}
#A;wrap (~' wrap)
#A;apply (~ g!apply)}
#join (~ g!join)}
(~ body'))))
#;Nil)]))
_
(#;Left "Wrong syntax for do")))
## [Functions]
(def: #export (seqM monad xs)
{#;doc "Run all the monadic values in the list and produce a list of the base values."}
(All [M a]
(-> (Monad M) (List (M a)) (M (List a))))
(case xs
#;Nil
(:: monad wrap #;Nil)
(#;Cons x xs')
(do monad
[_x x
_xs (seqM monad xs')]
(wrap (#;Cons _x _xs)))
))
(def: #export (mapM monad f xs)
{#;doc "Apply a monad-producing function to all values in a list."}
(All [M a b]
(-> (Monad M) (-> a (M b)) (List a) (M (List b))))
(case xs
#;Nil
(:: monad wrap #;Nil)
(#;Cons x xs')
(do monad
[_x (f x)
_xs (mapM monad f xs')]
(wrap (#;Cons _x _xs)))
))
(def: #export (foldM monad f init xs)
{#;doc "Fold a list with a monad-producing function."}
(All [M a b]
(-> (Monad M) (-> b a (M a)) a (List b)
(M a)))
(case xs
#;Nil
(:: monad wrap init)
(#;Cons x xs')
(do monad
[init' (f x init)]
(foldM monad f init' xs'))))
(def: #export (liftM Monad<M> f)
{#;doc "Lift a normal function into the space of monads."}
(All [M a b]
(-> (Monad M) (-> a b) (-> (M a) (M b))))
(lambda [ma]
(do Monad<M>
[a ma]
(wrap (f a)))))
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